The storage capacity of the DHW tank depends on the daily
water demand and the combination method. The daily water
demand is estimated with the following calculation formula
for consumption:
D
(T)= D
(60 °C) x (60-T
i
i
Where:
D
Water demand at T temperature
(T):
i
D
Domestic hot water demand at 60 °C
(60°C):
i
T:
Temperature of the DHW tank
T
Temperature of the inlet cold water
:
i
- Calculation of D
(60 °C):
i
The standard consumption, expressed in daily liters per
person and determined by technical installation regulations
of each country, is used to calculate the domestic hot water
demand at 60 °C, D
(60 °C). This quantity is then multiplied
i
by the expected number of users of the installation. In the
following example, the domestic hot water demand at 60 °C
has been considered as 30 liters per person, in a detached
house with 4 residents.
- Calculation of T:
The temperature of the DHW tank refers to the temperature
of the accumulated water inside the tank, prior to operation.
This temperature is usually between 45 °C and 65 °C. It has
been considered as 45 °C in this example.
- Calculation of Ti:
The temperature of the inlet cold water refers to the
temperature of the water being supplied to the tank. Since
this temperature is usually between 10 °C and 15 °C, it has
been considered as 12 °C in this example.
- Example:
Di(T)= 30 x 4 x (60-12 / 45-12) = 174.5 liters/day
174.5 x 2(*) = 349 liters/day approximate demand of hot
water
(*) It is recommended to multiply the calculated consumption by two,
in case that the installation is in a detached house. This is done to
ensure a steady supply of hot water. In the case of a multifamily
installation, it is not necessary to increase the forecast of hot water
demand, given the lower simultaneity factor.
/ T-T
)
i
i
23
SPACE HEATING/COOLING AND DHW